I have no idea what level they have him reading and are testing at but *I* failed multiple comprehension quizzes at the back of my kid's lower level readers. I would read along with my DD, be too bored to retain anything and then get to questions at the end that half the time weren't even about the text but were about extra details from the pictures!! ("What colour is mama bear's scarf?").

Is it possible to test his comprehension at the level he reads at home just to see what happens? They don't test 5th grader's reading comprehension skills on kindy books, but kindy kids reading at a 5th grade level have to be able to prove they still have "comprehension" skills that they either never needed or have long since forgotten.